Deck 11: Electrochemistry

Question 1

How many electrons are transferred in the following reaction?
SO₃^2-(aq) + MnO₄^-(aq) → SO₄^2-(aq) + Mn²⁺(aq)

A) 4
B) 10
C) 3
D) 2
E) 6

Answer 1

10

Question 2

The standard potential for the reaction Zn + 2Ag⁺ → Zn²⁺ + 2Ag is 1.56 V. Given that the standard reduction potential for Ag⁺ + e^- → Ag is 0.80 V, determine the standard reduction potential for Zn²⁺ + 2e^- → Zn.

A) 0.04 V
B) -0.38 V
C) -0.76 V
D) 0.76 V
E) none of these

Answer 2

-0.76 V

Question 3

Determine the standard potential, E°, of a cell that employs the reaction
Co + Ag⁺ → Co²⁺ +Ag

A) 1.88 V
B) -1.08 V
C) 1.08 V
D) -0.52 V
E) none of these

Answer 3

1.08 V

Question 4

The following questions refer to a galvanic cell that utilizes the following reaction (unbalanced):(AuCl₄)^-(aq) + Cu(s) → Au(s) + Cl^-(aq) + Cu²⁺(aq)
Determine the number of electrons transferred during the reaction (when balanced).

A) 2
B) 6
C) 4
D) 3
E) 9

Question 5

The following two half-reactions take place in a galvanic cell. At standard conditions, what species are produced at each electrode?

A) Sn is produced at the cathode, and Cu²⁺ is produced at the anode.
B) Cu is produced at the anode, and Sn²⁺ is produced at the cathode.
C) Cu is produced at the cathode, and Sn²⁺ is produced at the anode.
D) Sn is produced at the anode, and Cu is produced at the cathode.
E) Sn is produced at the anode, and Cu²⁺ is produced at the cathode.

Question 6

When the equation for the following reaction in basic solution is balanced, what is the sum of the coefficients?
MnO₄^-(aq) + CN^-(aq) → MnO₂(s) + CNO^-(aq)

A) 20
B) 10
C) 8
D) 13
E) 11

Question 7

What is the oxidation state of Mn in MnO₄^-?

A) 1
B) 9
C) 7
D) -1
E) 3

Question 8

Which of the following is the best reducing agent?

A) Cl^-
B) Cl₂
C) H₂
D) Mg
E) Mg²⁺

Question 9

Silver will spontaneously reduce which of the following?

A) Fe²⁺
B) Na⁺
C) Al³⁺
D) Co²⁺
E) none of these

Question 10

How many electrons are transferred in the following reaction?
2Cr₂O₇^2- + 14H⁺ + 6Cl^- → 2Cr³⁺ + 3Cl₂ + 7H₂O

A) 4
B) 2
C) 8
D) 6
E) none of these

Question 11

Which metal, Al or Ni, could reduce Zn²⁺ to Zn(s) if placed in a Zn²⁺(aq) solution?

A) Ni
B) Al
C) Both Al and Ni would work.
D) Neither Al nor Ni would work.
E) This cannot be determined.

Question 12

Refer to the galvanic cell below (the contents of each half-cell are written beneath each compartment). The standard reduction potentials are as follows:
What is the oxidation state of Cr in Cr₂O₇^2-?

A) +6
B) -2
C) +12
D) -1
E) +7

Question 13

The following questions refer to a galvanic cell that utilizes the following reaction (unbalanced):(AuCl₄)^-(aq) + Cu(s) → Au(s) + Cl^-(aq) + Cu²⁺(aq)
Given the following information, determine the standard cell potential.

A) 1.159 V
B) 2.102 V
C) 1.979 V
D) 1.462 V
E) 1.837 V

Question 14

Ammonium metavanadate reacts with sulfur dioxide in acidic solution as follows (hydrogen ions and H₂O omitted):
XVO₃^- + ySO₂ → xVO²⁺ + ySO₄^2-
The ratio x : y is

A) 1 : 3
B) 1 : 2
C) 2 : 1
D) 3 : 1
E) 1 : 1

Question 15

Which of the following is the strongest oxidizing agent?

A) Zn²⁺
B) I₂
C) MnO₄^-
D) Zn
E) MnO₂

Question 16

The following reaction occurs in basic solution:
Ag⁺ + Cu → Ag + Cu²⁺
When the equation is balanced, what is the sum of the coefficients?

A) 7
B) 6
C) 5
D) 4
E) 8

Question 17

A strip of copper is placed in a 1 M solution of copper nitrate, and a strip of silver is placed in a 1 M solution of silver nitrate. The two metal strips are connected to a voltmeter by wires, and a salt bridge connects the solutions. The following standard reduction potentials apply: When the voltmeter is removed and the two electrodes are connected by a wire, which of the following does not take place?

A) Negative ions pass through the salt bridge from the silver half-cell to the copper half-cell.
B) The silver electrode increases in mass as the cell operates.
C) Electrons flow in the external circuit from the copper electrode to the silver electrode.
D) Some positive copper ions pass through the salt bridge from the copper half-cell to the silver half-cell.
E) There is a net general movement of silver ions through the salt bridge to the copper half-cell.

Question 18

The reaction below occurs in basic solution. In the balanced equation, what is the sum of the coefficients?
Zn + NO₃^- → Zn(OH)₄^2- + NH₃

A) 27
B) 19
C) 23
D) 12
E) 15

Question 19

Which of the following would be the best reducing agent?

A) F^-
B) F₂
C) Na⁺
D) Cl₂
E) Na

Question 20

When the equation for the following reaction in basic solution is balanced, what is the sum of the coefficients?
MnO₂ + HO₂^- → MnO₄^-

A) 11
B) 9
C) 18
D) 31
E) 14

Question 21

The reaction Cr(s) + NO₃^-(aq) → Cr³⁺(aq) + NO(g) takes place in acidic solution.
How many electrons are transferred per mole of NO(g)?

A) 4
B) 2
C) 3
D) 5
E) 1

Question 22

Consider an electrochemical cell with a copper electrode immersed in 1.0 M Cu²⁺ and a silver electrode immersed in 1.0 M Ag⁺.
Which of the electrodes is the anode?

A) the silver electrode
B) the copper electrode

Question 23

In a common car battery, six identical cells each carry out the following reaction:
Pb + PbO₂ + 2HSO₄^- + 2H⁺ → 2PbSO₄ + 2H₂O
For such a cell, E° is 2.04 V. Calculate ΔG° at 25°C.

A) -787 kJ
B) -197 kJ
C) -394 kJ
D) -98 kJ
E) -0.121 kJ

Question 24

In which direction do electrons flow in the external circuit?

A) right to left
B) left to right
C) No current flows; the cell is at equilibrium.

Question 25

The reduction potentials for Au³⁺ and Ni²⁺ are as follows:
Au³⁺ + 3e^- → Au E° = +1.50 V
Ni²⁺ + 2e^- → Ni E° = -0.23 V
Calculate ΔG° (at 25°C) for the reaction
2Au³⁺ + 3Ni → 3Ni²⁺ + 2Au

A) -1.00 × 10³ kJ
B) -2140 kJ
C) +5.00 × 10² kJ
D) -5.00 × 10² kJ
E) +1.00 × 10³ kJ

Question 26

How many electrons are transferred in the balanced reaction (that is, what will be the value of n in the Nernst equation)?

A) 22
B) 30
C) 2
D) 6
E) 5

Question 27

Refer to the galvanic cell below (the contents of each half-cell are written beneath each compartment). The standard reduction potentials are as follows:
When current is allowed to flow, which species is reduced?

A) H⁺
B) MnO₄^-
C) Cr³⁺
D) Mn²⁺
E) Cr₂O₇^2-

Question 28

Choose the correct statement(s) given the following information:
I.Fe²⁺(aq) is more likely to be oxidized than Fe²⁺ complexed to CN^-.
II.Fe³⁺(aq) is more likely to be reduced than Fe³⁺ complexed to CN^-.
III.Complexation of Fe ions with CN^- has no effect on their tendencies to become
Oxidized or reduced.

A) I and II
B) II only
C) I only
D) III only
E) None of these is true.

Question 29

The reaction Cr(s) + NO₃^-(aq) → Cr³⁺(aq) + NO(g) takes place in acidic solution.
What is the coefficient of H₂O(l) in the balanced equation?

A) 3
B) 5
C) 4
D) 2
E) 1

Question 30

Consider an electrochemical cell with a copper electrode immersed in 1.0 M Cu²⁺ and a silver electrode immersed in 1.0 M Ag⁺.
Calculate E° for this cell.

A) 0.46 V
B) 1.14 V
C) 1.26 V
D) 1.48 V
E) none of these

Question 31

Consider the galvanic cell shown below (the contents of each half-cell are written beneath each compartment). The standard reduction potentials are as follows:
Which of the following statements about this cell is false?

A) To complete the circuit, cations migrate into the left half-cell and anions migrate into the right half-cell from the salt bridge.
B) This is a galvanic cell.
C) Electrons flow from the Pt electrode to the Cr electrode.
D) The cell is not at standard conditions.
E) Reduction occurs at the Pt electrode.

Question 32

The standard free energies of formation of several aqueous species are What is the standard reduction potential of methanoic acid in aqueous solution (that is, for HCOOH + 4H⁺ + 4e^- → CH₃OH + H₂O)?

A) +0.13 V
B) +0.25 V
C) -0.25 V
D) -0.13 V
E) +0.17 V

Question 33

Consider the hydrogen-oxygen fuel cell where
H₂(g) + O₂(g) H₂O(l)
ΔG° = -237.18 kJ/mol H₂
Which of the following statements is(are) true?
I.At standard conditions, the maximum work the fuel cell could do on the surroundings
Is 237.18 kJ/mol.
II.In the real world, the actual amount of useful work the cell can do is less than 237.18 kJ.
III.More energy is dissipated as waste heat in the fuel cell than in the reversible pathway.

A) I
B) I, II, and III
C) II
D) III
E) None of the statements is true.

Question 34

Consider the following reduction potentials: For a galvanic cell employing the Cu, Cu²⁺ and Pb, Pb²⁺ couples, calculate the maximum amount of work that would accompany the reaction of 1 mol of lead under standard conditions.

A) -90.7 kJ
B) No work can be done. The system is at equilibrium.
C) -40.5 kJ
D) -45.3 kJ
E) none of these

Question 35

Consider the galvanic cell shown below (the contents of each half-cell are written beneath each compartment). The standard reduction potentials are as follows:
What is E° for this cell?

A) 0.36 V
B) 4.40 V
C) 1.79 V
D) 1.82 V
E) 4.75 V

Question 36

Refer to the galvanic cell below (the contents of each half-cell are written beneath each compartment). The standard reduction potentials are as follows:
When current is allowed to flow, which species is oxidized?

A) Mn²⁺
B) Cr³⁺
C) MnO₄^-
D) Cr₂O₇^2-
E) H⁺

Question 37

Refer to the galvanic cell below (the contents of each half-cell are written beneath each compartment). The standard reduction potentials are as follows:
What is the value of E°_cell?

A) 2.84 V
B) 0.18 V
C) -0.18 V
D) 1.79 V
E) 2.29 V

Question 38

In which of the following cases must E be equal to zero?
I.In any cell at equilibrium
II.In a concentration cell
III.E° can never be equal to zero.

A) II only
B) I and II
C) III
D) I only

Question 39

In which of the following cases can E° be equal to zero?
I.In any cell at equilibrium
II.In a concentration cell
III.E° can never be equal to zero.

A) I only
B) III
C) I and II
D) II only

Question 40

Refer to the galvanic cell below (the contents of each half-cell are written beneath each compartment). The standard reduction potentials are as follows:
In the balanced cell reaction, what is the stoichiometric coefficient for H⁺?

A) 5
B) 30
C) 22
D) 2
E) 6

Question 41

A concentration cell is constructed using two Ni electrodes with Ni²⁺ concentrations of 1.66 M and 1.60 × 10^-4 M in the two half-cells. The reduction potential of Ni²⁺ is -0.23 V. Calculate the potential of the cell at 25°C.

A) -0.237 V
B) +0.119 V
C) +0.349 V
D) -0.273 V
E) 0.0073 V

Question 42

Consider an electrochemical cell that has a nickel electrode immersed in 1.0 M Ni²⁺ and a platinum electrode immersed in 0.010 M Co²⁺.
Calculate E for this cell.

A) 0.51 V
B) 0.56 V
C) 0.05 V
D) 0.11 V
E) none of these

Question 43

​The standard potential for the reaction A(s) + B³⁺ (aq) A³⁺ (aq​) + B (​s​) is 0.49 V. What is the equilibrium constant K for this reaction at 25°C?

A) ​0.015
B) ​7.7×10^-26
C) ​17
D) ​1.3×10²⁵
E) ​-17

Question 44

An excess of finely divided iron is stirred up with a solution that contains Cu²⁺ ion, and the system is allowed to come to equilibrium. The solid materials are then filtered off, and electrodes of solid copper and solid iron are inserted into the remaining solution. What is the value of the ratio [Fe²⁺]/[Cu²⁺] at 25°C?

A) 1
B) 2.5 × 10²⁶
C) 0
D) 4.0 × 10^-27
E) none of these

Question 45

A fuel cell designed to react grain alcohol with oxygen has the following net reaction:
C₂H₅OH(l) + 3O₂(g) → 2CO₂(g) + 3H₂O(l)
The maximum work that 1 mol of alcohol can yield by this process is 1320 kJ. What is the theoretical maximum voltage this cell can achieve?

A) 1.14 V
B) 2.28 V
C) 13.7 V
D) 2.01 V
E) 0.760 V

Question 46

Refer to the galvanic cell below (the contents of each half-cell are written beneath each compartment). The standard reduction potentials are as follows:
What is the cell potential at 25°C as read on the digital voltmeter?

A) 0.18 V
B) 2.58 V
C) 0.59 V
D) 0.10 V
E) 0.26 V

Question 47

For a reaction in a voltaic cell, both ΔH° and ΔS° are positive. Which of the following statements is true?

A) E°_cell will increase with an increase in temperature.
B) E°_cell will decrease with an increase in temperature.
C) E°_cell will not change when the temperature increases.
D) ΔG° > 0 for all temperatures.
E) None of the above statements is true.

Question 48

Consider an electrochemical cell that has a nickel electrode immersed in 1.0 M Ni²⁺ and a platinum electrode immersed in 0.010 M Co²⁺.
Calculate the concentration of Ni²⁺ if the cell is allowed to run to equilibrium at 25°C.

A) 1.0 M
B) 1.1 M
C) 1.9 × 10^-4 M
D) 0.020 M
E) none of these

Question 49

If a reducing agent M reacts with an oxidizing agent A⁺ to give M⁺ and A, and the equilibrium constant for the reaction is 1.0, then what is the E° value for the oxidation-reduction reaction at 25°C?

A) 0.059 V
B) 1.0 V
C) 0.0 V
D) 0.68 V
E) -1.0 V

Question 50

Consider the galvanic cell shown below (the contents of each half-cell are written beneath each compartment). The standard reduction potentials are as follows:
What is the value of E for this cell at 25°C?

A) 1.88 V
B) 2.12 V
C) 1.76 V
D) 2.21 V
E) 0.59 V

Question 51

An excess of finely divided iron is stirred up with a solution that contains Cu²⁺ ion, and the system is allowed to come to equilibrium. The solid materials are then filtered off, and electrodes of solid copper and solid iron are inserted into the remaining solution. What potential develops between these two electrodes at 25°C?

A) 0
B) 0.592 V
C) 0.296 V
D) -0.78 V
E) Not enough information is given.

Question 52

A cell is set up with copper and lead electrodes in contact with CuSO₄(aq) and Pb(NO₃)₂(aq), respectively, at 25°C. The standard reduction potentials are
Pb²⁺ + 2e^- → Pb E° = -0.13 V
Cu²⁺ + 2e^- → Cu E° = +0.34 V
If sulfuric acid is added to the Pb(NO₃)₂ solution, forming a precipitate of PbSO₄, the cell potential

A) It is impossible to tell what will happen.
B) decreases.
C) is unchanged.
D) increases.

Question 53

Consider an electrochemical cell with a copper electrode immersed in 1.0 M Cu²⁺ and a silver electrode immersed in 1.0 M Ag⁺. ​
If [Cu²⁺]₀ is 0.0038 M and [Ag⁺]₀ is 0.27 M, calculate E.

A) 0.41 V
B) 0.50 V
C) 0.42 V
D) 0.51 V
E) 0.59 V

Question 54

Refer to the galvanic cell below (the contents of each half-cell are written beneath each compartment). The standard reduction potentials are as follows:
What is the value of Q, the reaction quotient, for this cell reaction?

A) 1.5 × 10^-4
B) 6.7 × 10³
C) 6.7 × 10⁴⁰
D) 1.5 × 10^-41

Question 55

You make a cell with a copper electrode in a solution of copper nitrate and a silver electrode in a solution of silver nitrate.
If you could increase the concentration of Cu²⁺, which of the following would be true about the cell potential?

A) It would remain constant.
B) This cannot be determined.
C) It would increase.
D) It would decrease.

Question 56

Determine the equilibrium constant at 25°C for the reaction
Zn + Ni²⁺ → Zn²⁺ + Ni

A) 4.1 × 10³
B) 9.3 × 10⁸
C) 8.6 × 10¹⁷
D) 6.4 × 10^-6
E) none of these

Question 57

A galvanic cell is constructed with copper electrodes and Cu²⁺ in each compartment. In one compartment, [Cu²⁺] = 2.4 × 10^-3 M, and in the other compartment, [Cu²⁺] = 3.0 M. Calculate the potential for this cell at 25°C. The standard reduction potential for Cu²⁺ is +0.34 V.

A) 0.77 V
B) 0.092 V
C) -0.092 V
D) -0.43 V
E) 0.43 V

Question 58

A concentration cell is constructed using two Co electrodes with Co²⁺ concentrations of 0.20 M and 3.6 × 10^-5 M in the two half-cells. Determine the standard reduction potential of Co²⁺, given that the potential of the cell at 25°C is 0.111 V.

A) +0.221 V
B) +0.111 V
C) -0.111 V
D) This cannot be determined with the information given.
E) 0 V

Question 59

Refer to the galvanic cell below (the contents of each half-cell are written beneath each compartment). The standard reduction potentials are as follows:
What is the value of the equilibrium constant at 25°C for the net spontaneous cell reaction?

A) 7.3 × 10^-11
B) 4.3 × 10^-92
C) 1.1 × 10³
D) 91
E) 2.3 × 10⁹¹

Question 60

You make a cell with a copper electrode in a solution of copper nitrate and a silver electrode in a solution of silver nitrate.
If you could increase the concentration of Ag⁺, which of the following would be true about the cell potential?

A) This cannot be determined.
B) It would increase.
C) It would remain constant.
D) It would decrease.

Question 61

In a common car battery, six identical cells each carry out the following reaction:
Pb + PbO₂ + 2HSO₄^- + 2H⁺ → 2PbSO₄ + 2H₂O
​
Suppose that to start a car on a cold morning, 138 amperes is drawn for 12.0 seconds from such a cell. How many grams of Pb are consumed? (The atomic mass of Pb is 207.19 g/mol.)

A) 0.562 g
B) 7.11 g
C) 1.78 g
D) 0.01235 g
E) 3.56 g

Question 62

Calculate E at 25°C for this cell, given the following data: Ag⁺ + e^- → Ag(s) E° = 0.80 V
Ni²⁺ + 2e^- → Ni(s) E° = -0.23 V
K_sp for AgCl = 1.6 × 10^-10

A) 2.98 V
B) This cannot be determined from the data given
C) 0.83 V
D) 1.01 V
E) 0.54 V

Question 63

Fe²⁺ + 2e^- → Fe(s) E° = -0.440 V
2H⁺ + 2e^- → H₂(g) E° = 0.000 V
In a galvanic cell, the iron compartment contains an iron electrode, and [Fe²⁺] = 1.00 × 10^-3 M. The hydrogen compartment contains a platinum electrode (P_H2 = 1.00 atm) and a weak acid HA at an initial concentration of 1.00 M. If the observed cell potential is 0.333 V at 25°C, calculate K_a for the weak acid HA at 25°C.

Question 64

An antique automobile bumper is to be chrome plated. The bumper, which is dipped into an acidic Cr₂O₇^2- solution, serves as a cathode of an electrolytic cell. The atomic mass of Cr is 51.996; 1 faraday = 96,485 coulombs.
If oxidation of H₂O occurs at the anode, how many moles of oxygen gas will evolve for every 3.30 × 10² g of Cr(s) deposited?

A) 8.46 mol
B) 9.52 mol
C) 4.23 mol
D) 6.35 mol
E) 3.17 mol

Question 65

A solution of MnO₄^2- is electrolytically reduced to Mn³⁺. A current of 8.46 amp is passed through the solution for 15.0 minutes. What is the number of moles of Mn³⁺ produced in this process? (1 faraday = 96,485 coulombs)

A) 0.000438 mol
B) 0.0197 mol
C) 0.0789 mol
D) 0.0395 mol
E) 0.0263 mol

Question 66

If an electrolysis plant operates its electrolytic cells at a total current of 1.0 × 10⁶ amp, how long will it take to produce one metric ton (one million grams) of Mg(s) from seawater containing Mg²⁺? (1 faraday = 96,485 coulombs)

A) 55 min
B) 3.7 h
C) 2.2 h
D) 1 year
E) 2.4 days

Question 67

How many seconds would it take to deposit 21.40 g of Ag (atomic mass = 107.87) from a solution of AgNO₃ using a current of 10.00 amp?

A) 4825 s
B) 9649 s
C) 3828 s
D) 1914 s
E) none of these

Question 68

If a constant current of 5.2 amperes is passed through a cell containing Cr³⁺ for 2.1 hour, how many grams of Cr will plate out onto the cathode? (The atomic mass of Cr is 51.996 g/mol.)

A) 0.12 g
B) 1.1 g
C) 64 g
D) 21 g
E) 7.1 g

Question 69

What quantity of charge is required to reduce 32.6 g of CrCl₃ to chromium metal? (1 faraday = 96,485 coulombs)

A) 3.97 × 10⁴ C
B) 7.95 × 10⁴ C
C) 5.96 × 10⁴ C
D) 1.81 × 10⁵ C
E) 1.99 × 10⁴ C

Question 70

Use the following data to calculate the K_sp value at 25°C for PbSO₄(s).

A) 3.89 × 10^-105
B) 2.57 × 10¹⁰⁵
C) 1.7 × 10^-8
D) 5.9 × 10⁷
E) None of these is within 5% of the correct answer.

Question 71

An electrolytic cell process involves plating Zr(s) from a solution containing Zr⁴⁺. If 5.80 amp is run through this mixture for 1.86 h, what mass of Zr is plated?

A) 36.7 g
B) 9.18 g
C) 0.153 g
D) 0.101 g
E) none of these

Question 72

Electrolysis of a molten salt with the formula MCl, using a current of 3.86 amp for 16.2 min, deposits 1.52 g of metal. Identify the metal. (1 faraday = 96,485 coulombs)

A) Rb
B) Na
C) Li
D) Ca
E) K

Question 73

Why is aluminum protected from corrosion? (Note: The standard reduction potential for Al³⁺ is -1.66 V.)

A) Oxygen and aluminum have no affinity for one another.
B) The oxidation of aluminum is not a favored process, as seen by the standard reduction potential for Al³⁺.
C) Aluminum forms a protective oxide coating.
D) At least two of these are correct.
E) Aluminum is not protected from corrosion.

Question 74

Ag⁺ + e^- ? Ag(s) E° = 0.80 V
Cu²⁺ + 2e^- ? Cu(s) E° = 0.34 V
In a galvanic cell, the silver compartment contains a silver electrode and excess AgCl(s) (K_sp = 1.6 × 10^-10). The copper compartment contains a copper electrode, and [Cu²⁺] = 2.0 M.

A. Calculate the potential for this cell at 25°C.
B. Assuming 1.0 L of 2.0 M Cu²⁺ in the copper compartment, calculate how many moles of NH₃ would have to be added to establish the cell potential at 0.52 V at 25°C (assume no volume change on addition of NH₃).
Cu²⁺ + 4NH₃ Cu(NH₃)₄S1U112+ K_f = 1.0 ×10¹³

Question 75

Copper is electroplated from an aqueous CuSO₄ solution. A constant current of 4.70 amp is applied by an external power supply. How long will it take to deposit 3.76 × 10² g of Cu? The atomic mass of copper is 63.546 g/mol.

A) 33.7 h
B) 101.2 h
C) 2.08 h
D) 67.5 h
E) 135.0 h

Question 76

Calculate the solubility product of silver iodide at 25°C, given the following data:

A) 1.9 × 10^-4
B) 8.4 × 10^-17
C) 3.5 × 10^-20
D) 2.9 × 10^-3
E) 2.1 × 10^-12

Question 77

An antique automobile bumper is to be chrome plated. The bumper, which is dipped into an acidic Cr₂O₇^2- solution, serves as a cathode of an electrolytic cell. The atomic mass of Cr is 51.996; 1 faraday = 96,485 coulombs.
If the current is 18.8 amperes, how long will it take to deposit 1.66 × 10² g of Cr(s) onto the bumper?

A) 27.3 h
B) 13.4 h
C) 45.5 min
D) 18.2 h
E) 54.6 h

Question 78

Gold (atomic mass = 197 g/mol) is plated from a solution of chlorauric acid, HAuCl₄; it deposits on the cathode. Calculate the time it takes to deposit 0.55 g of gold, passing a current of 0.12 amperes. (1 faraday = 96,485 coulombs)

A) 0.0018 days
B) 0.62 h
C) 1.9 h
D) 2.5 h
E) 1.2 h

Question 79

Nickel is electroplated from a NiSO₄ solution. A constant current of 5.72 amp is applied by an external power supply. How long will it take to deposit 2.08 × 10² g of Ni? (The atomic mass of Ni is 58.69 g/mol.)

A) 16.6 h
B) 33.2 h
C) 1.51 h
D) 19.9 min
E) 49.8 h

Question 80

Gold is produced electrochemically from an aqueous solution of Au(CN)₂^- containing an excess of CN^-. Gold metal and oxygen gas are produced at the electrodes. How many moles of O₂ will be produced during the production of 1.00 mol of gold?

A) 4.00 mol
B) 3.56 mol
C) 0.50 mol
D) 1.00 mol
E) 0.25 mol